新型碳纳米多孔材料，包括碳纳米管网络材料、石墨烯泡沫材料以及它们的复合材料，是由大量碳纳米管或者石墨烯片作为基本单元聚合而成的宏观块体多孔材料。这些多孔材料继承了碳管、石墨烯以及多孔材料的优点，具有优良的力学、电学、热学等性能，在光电器件、储能、环境、生物等众多前沿领域有着广阔的应用前景。目前，由于对该类多孔材料的变形以及性能调控机制缺乏充分认识，相关材料的设计改性与应用受到制约。本文建立了包含交联、考虑断裂等特性的碳纳米管网络材料、石墨烯泡沫材料以及石墨烯/碳纳米管复合多孔材料的力学模型，采用粗粒化分子动力学模拟与准静态实验相结合的手段，系统研究了这类碳纳米多孔材料在拉伸、压缩、剪切加载下的变形行为与断裂模式，重点考虑了单元间交联对材料宏观力学性能的影响机制，取得以下四方面成果：

（1）碳管网络材料的变形以及断裂模式。碳管网络材料在拉伸和压缩载荷下表现出不同的变形模式。在拉伸载荷下，当材料的交联密度超过某一临界值时，材料的变形模式由弯曲变形主导转变为弯曲-拉伸-弯曲三阶段主导模式。此外，存在另一临界交联密度，交联密度高于该临界值时材料由韧性断裂转变为脆性断裂。在压缩载荷下，材料的变形模式始终以碳管弯曲变形为主，与交联密度和压缩应变无关。

（2）石墨烯泡沫材料在简单剪切作用下的变形及断裂特征。石墨烯泡沫材料在剪切加载下呈现出明显的应变硬化特征。宏观应变硬化现象是由微观非局部断裂以及由此导致的石墨烯片的几何与应力重排布共同引发的。片间交联密度以及片层厚度可以对应变硬化特征进行调控。剪切刚度G随交联密度线性增加，与石墨烯片层数n之间满足标度率关系G ~ n^1.95。

（3）石墨烯泡沫材料塑性变形的微结构机理。提出“变形不均匀度”参数，并基于该指标揭示了石墨烯泡沫在拉伸作用下的“非局部塑性-局部塑性”二阶段塑性变形特征。拉伸应变小于临界值时，全局分布的不可逆微结构变化导致非局部塑性变形；超过临界应变后，断裂带附近集中出现的不可逆断键造成的局部变形成为主要的塑性来源。在压缩作用下材料中仅发生非局部塑性变形。

（4）石墨烯/碳纳米管复合材料的力学性能与调控机理。模拟和实验研究结果表明，相较于石墨烯泡沫，复合材料的拉伸强度、最大可拉伸应变、压缩刚度与压缩回弹性能均显著提高。从微结构演化的角度分析，碳管具有增强增韧、避免石墨烯片贴合的作用，因此可以改善复合材料性能。基于“变形不均匀度”参数，发现复合材料在拉伸作用下存在非局部塑性与局部塑性变形两个阶段。非局部塑性变形由全局分布的不可逆微结构变化导致；在局部塑性变形阶段内，石墨烯分离造成的断裂弱面出现后，碳管的不可逆伸长为局部塑性的主要来源。

上述结果为提升和优化碳纳米多孔材料的物理力学性能提供科学依据，对该类材料的性能优化以及工程应用具有重要的指导价值。

New porous carbon nanomaterials, including carbon nanotube networks, graphene foams and their hybrid materials, are macro-porous bulk materials made up of a large number of carbon nanotubes or graphene sheets as building blocks. These new porous materials inherit the advantages of carbon nanotube, graphene and porous structure, having a series of excellent mechanical, electrical and thermal properties, leading broad application prospects in many fields such as optoelectronic devices, energy storage, environment, biology and so on. At present, the mechanical mechanism and the tuning scheme of this new kind of porous materials are elusive, which greatly restricts their designs and applications. In this dissertation, the mechanical models of carbon nanotube networks, graphene foams, graphene/carbon nanotube hybrid materials with crosslinks are established in consideration of bond-breakings. Using coarse-grained molecular dynamics simulation and quasi-static mechanical experiments, the deformation behaviors and fracture modes of these new porous carbon materials under tension, compression and shear loading are systematically studied. The effect of the building blocks and crosslinks on the mechanical properties of the assemblies is discussed. The main work of this dissertation is as follows:

(1) Deformation and fracture modes of carbon nanotube networks. Carbon nanotube networks show different deformation modes under tensile and compressive loadings. Under tensile loading, there is a critical crosslink density tuning the deformation mode from bend-dominant to bend-stretch-bend-dominant three-stage mode. In addition, there is another critical crosslink density tuning the fracture mode from ductile to brittle fracture with increasing crosslink density. Under compressive loading, the deformation mode of the material is always bend-dominated, independent of crosslink density and compressive strain.

(2) Deformation and fracture characteristics of graphene foams under simple shear loading. Graphene foams exhibit strain hardening characteristic under shear loading. The strain hardening phenomenon in macroscopic scale is caused by the microscopic non-localized fractures and the resulting rearrangements of graphene sheets and the redistribution of stresses. The strain hardening can be controlled by crosslink density and graphene layers. The shear stiffness G increases linearly with crosslink density, and the relationship between G and the number of graphene layers n satisfies G ~ n^1.95.

(3) Micro-structural mechanism of the plasticity of graphene foams. The parameter of "non-uniformity of deformation" is proposed to unveil that the plastic deformation of graphene foams under tension has two successive stages characterized by the non-localized and localized microscopic plasticity, respectively. When the tensile strain is smaller than a critical value, the plasticity of graphene foams is dominated by the non-localized irreversible changes of micro-structures; when the tensile strain exceeds the critical value, it is dominated by the localized plastic deformation caused by irreversible bond-breakings near the fracture zone. Furthermore, we find that only non-localized plasticity occurs in graphene foams under compression.

(4) Mechanical properties and tuning scheme of graphene/carbon nanotube hybrid materials. We find experimentally that the strength, ductility and resilience of the composite can be improved by adding a fraction of carbon nanotubes, and the three underlying mechanisms are strengthening, toughening and avoiding the accumulation of graphene sheets caused by carbon nanotubes. According to the parameter of the "non-uniformity of deformation", the tensile deformation of the composite includes two successive stages characterized by non-localized and localized plastic deformation, respectively. The non-localized microscopic plasticity is similar to that in the pristine graphene foams in the above section. In the localized plastic deformation stage, the irreversible elongation of carbon nanotubes is the main source of plasticity.

These results provide a scientific basis for improving and optimizing the physical and mechanical properties of carbon-based porous materials, and can guide the performance optimization and engineering application of this new kind of materials